tools lib bpf: Extract and collect map names from BPF object file

This patch collects name of maps in BPF object files and saves them into
'maps' field in 'struct bpf_object'. 'bpf_object__get_map_by_name' is
introduced to retrive fd and definitions of a map through its name.

Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: He Kuang <hekuang@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1448614067-197576-3-git-send-email-wangnan0@huawei.com
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 65 insertions, 3 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f50982579aa8..a298614ad091 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -165,6 +165,7 @@ struct bpf_program {
 
 struct bpf_map {
         int fd;
+        char *name;
         struct bpf_map_def def;
         void *priv;
         bpf_map_clear_priv_t clear_priv;
@@ -526,12 +527,46 @@ bpf_object__init_maps(struct bpf_object *obj, void *data,
         return 0;
 }
 
+static void
+bpf_object__init_maps_name(struct bpf_object *obj, int maps_shndx)
+{
+        int i;
+        Elf_Data *symbols = obj->efile.symbols;
+
+        if (!symbols || maps_shndx < 0)
+                return;
+
+        for (i = 0; i < symbols->d_size / sizeof(GElf_Sym); i++) {
+                GElf_Sym sym;
+                size_t map_idx;
+                const char *map_name;
+
+                if (!gelf_getsym(symbols, i, &sym))
+                        continue;
+                if (sym.st_shndx != maps_shndx)
+                        continue;
+
+                map_name = elf_strptr(obj->efile.elf,
+                                      obj->efile.ehdr.e_shstrndx,
+                                      sym.st_name);
+                map_idx = sym.st_value / sizeof(struct bpf_map_def);
+                if (map_idx >= obj->nr_maps) {
+                        pr_warning("index of map \"%s\" is buggy: %zu > %zu\n",
+                                   map_name, map_idx, obj->nr_maps);
+                        continue;
+                }
+                obj->maps[map_idx].name = strdup(map_name);
+                pr_debug("map %zu is \"%s\"\n", map_idx,
+                         obj->maps[map_idx].name);
+        }
+}
+
 static int bpf_object__elf_collect(struct bpf_object *obj)
 {
         Elf *elf = obj->efile.elf;
         GElf_Ehdr *ep = &obj->efile.ehdr;
         Elf_Scn *scn = NULL;
-        int idx = 0, err = 0;
+        int idx = 0, err = 0, maps_shndx = -1;
 
         /* Elf is corrupted/truncated, avoid calling elf_strptr. */
         if (!elf_rawdata(elf_getscn(elf, ep->e_shstrndx), NULL)) {
@@ -581,10 +616,11 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                         err = bpf_object__init_kversion(obj,
                                                         data->d_buf,
                                                         data->d_size);
-                else if (strcmp(name, "maps") == 0)
+                else if (strcmp(name, "maps") == 0) {
                         err = bpf_object__init_maps(obj, data->d_buf,
                                                     data->d_size);
-                else if (sh.sh_type == SHT_SYMTAB) {
+                        maps_shndx = idx;
+                } else if (sh.sh_type == SHT_SYMTAB) {
                         if (obj->efile.symbols) {
                                 pr_warning("bpf: multiple SYMTAB in %s\n",
                                            obj->path);
@@ -625,6 +661,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                 if (err)
                         goto out;
         }
+
+        if (maps_shndx >= 0)
+                bpf_object__init_maps_name(obj, maps_shndx);
 out:
         return err;
 }
@@ -1086,6 +1125,7 @@ void bpf_object__close(struct bpf_object *obj)
         bpf_object__unload(obj);
 
         for (i = 0; i < obj->nr_maps; i++) {
+                zfree(&obj->maps[i].name);
                 if (obj->maps[i].clear_priv)
                         obj->maps[i].clear_priv(&obj->maps[i],
                                                 obj->maps[i].priv);
@@ -1266,6 +1306,13 @@ int bpf_map__get_def(struct bpf_map *map, struct bpf_map_def *pdef)
         return 0;
 }
 
+const char *bpf_map__get_name(struct bpf_map *map)
+{
+        if (!map)
+                return NULL;
+        return map->name;
+}
+
 int bpf_map__set_private(struct bpf_map *map, void *priv,
                          bpf_map_clear_priv_t clear_priv)
 {
@@ -1318,3 +1365,15 @@ bpf_map__next(struct bpf_map *prev, struct bpf_object *obj)
                 return NULL;
         return &obj->maps[idx];
 }
+
+struct bpf_map *
+bpf_object__get_map_by_name(struct bpf_object *obj, const char *name)
+{
+        struct bpf_map *pos;
+
+        bpf_map__for_each(pos, obj) {
+                if (strcmp(pos->name, name) == 0)
+                        return pos;
+        }
+        return NULL;
+}
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index ef631255dfaa..a51594c7b518 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -170,6 +170,8 @@ struct bpf_map_def {
  * it is not a uapi header so no need to consider name clash.
  */
 struct bpf_map;
+struct bpf_map *
+bpf_object__get_map_by_name(struct bpf_object *obj, const char *name);
 
 struct bpf_map *
 bpf_map__next(struct bpf_map *map, struct bpf_object *obj);
@@ -180,6 +182,7 @@ bpf_map__next(struct bpf_map *map, struct bpf_object *obj);
 
 int bpf_map__get_fd(struct bpf_map *map);
 int bpf_map__get_def(struct bpf_map *map, struct bpf_map_def *pdef);
+const char *bpf_map__get_name(struct bpf_map *map);
 
 typedef void (*bpf_map_clear_priv_t)(struct bpf_map *, void *);
 int bpf_map__set_private(struct bpf_map *map, void *priv,